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28-May-2008 Non-linear Beam Dynamics WS 1
On Injection Beam Loss
at
the SPring-8 Storage Ring
Masaru TAKAO
&
J. Schimizu, K. Soutome, and H. Tanaka
JASRI / SPring-8
28-May-2008 Non-linear Beam Dynamics WS 2
Outline
• Motivation
• SPring-8 storage ring
• Injection efficiency measurement
• Tracking simulation
• Improvement of injection efficiency– Beam collimation in transport line
– Low chromaticity operation
– Beta-distortion correction
• Summary
28-May-2008 Non-linear Beam Dynamics WS 3
Motivation
• Injection beam loss is a very important issue
for top-up operation.
– Demagnetization of insertion devices (ID)
– Radiation safety
• Before introducing top-up operation, we
intensively studied injection beam loss at the
Spring-8 storage ring.
– Effects of ID gap, chromaticity, beta-distortion, …
28-May-2008 Non-linear Beam Dynamics WS 4
SPring-8 Storage Ring Parameters
energy 8 GeV
circumference 1.5 km
horizontal / vertical betatron tune 40.15 / 18.35
horizontal / vertical chromaticity 8.0 / 8.3
natural emittance 3.4 nmrad
emittance coupling ratio 0.002
synchrotron tune 0.01
energy spread 0.0011
bunch length (zero current limit) 12.5 ps
@ 2002.9 ~ 2003.7
28-May-2008 Non-linear Beam Dynamics WS 5
Storage Ring Optics
• Modified Chasman-Green optics• 4 magnet-free straight sections of 30 m long• 36 normal cells, 4 long straight sections
-10
0
10
20
30
40
50
60
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0 50 100 150
Bet
atro
n F
un
ctio
n [
m]
Disp
ersion F
un
ction [m
]
Long Straight SectionNormalCG Cell
Path Length [m]
NormalCG Cell
xy
x
28-May-2008 Non-linear Beam Dynamics WS 6
Insertion Devices @ SPring-8
• 27 ID's– in-vacuum: 21, out-vacuum: 6.– One of in-vacuum undulators (ID19) is 2
5 m long.
standard ID long ID
in-vacuum ID
28-May-2008 Non-linear Beam Dynamics WS 7
Insertion Device Parameters
ID19 (long) ID20 (standard)
length 25 m 4.5 m
minimum gap 12 mm 7 mm
maximum gap 50 mm 50 mm
vertical beta @ center 14.1 m 5.6 m
vertical beta @ ends 25.2 m 6.5 m
cf. vacuum chamber height: 40 mm
28-May-2008 Non-linear Beam Dynamics WS 8
Injection Efficiency Measurement• Turn-by-turn current monitor
– ICT + oscilloscope.
– Used for study.
• Voltage sum of 4 electrodes of turn-by-turn BPM
– Influenced by synchrotron motion.
• (DCCT @ storage ring) - (BCM @ beam transport)
– Monitoring in user operation.
0.8
0.9
1
0 500 1000 1500 2000
current monitorBPM voltage sum
Inje
ctio
n E
ffic
ienc
y
Turn
28-May-2008 Non-linear Beam Dynamics WS 9
Experiments• Injection efficiency is measured for various ID gap.
– Use ID as a scraper.• Measured for ID19 (long), ID20, ID37 (standard).
0.6
0.7
0.8
0.9
1
0 500 1000 1500 2000
ID19
Inje
ctio
n E
ffic
ienc
y
Turn
12 mm
13 mm14 mm15 mm16 mm18 mm20 mm
50 mm ~ 22 mm
0.6
0.7
0.8
0.9
1
0 500 1000 1500 2000
ID20
Inje
ctio
n E
ffic
ienc
y
Turn
7 mm8 mm9 mm10 mm
50 mm ~ 11 mm
long undulator standard undulator
28-May-2008 Non-linear Beam Dynamics WS 10
Dependence of injection efficiency on ID gap• Gap where injection efficiency starts to decrease is different between l
ong undulator and standard ones.• The injection efficiencies corresponding to the same effective gaps of
ID's coincide.• The effective gap of injection efficiency starting to drop corresponds to
the minimum effective height of the vacuum chamber.• Injection efficiency is limited by transverse dynamics.
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50
ID19ID20ID37
Inje
ctio
n E
ffic
ien
cy
Gap [mm]
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20
ID19ID20ID37
Inje
ctio
n E
ffic
ien
cy
Effective Gap (Gap/y1/2) [mm/mm1/2]
Minimum effectivechamper height
28-May-2008 Non-linear Beam Dynamics WS 11
Tracking Simulation
• "Racetrack" based tracking code.
• 6 x 6 formalism.
• Symplectic integration.
• Using ring model (error fields) derived by response ma
trix analysis.
• With physical apertures.
• 1000 particles, 1000 revolutions.
28-May-2008 Non-linear Beam Dynamics WS 12
Injection Beam Parameters
horizontal emittance 220 nmrad
emittance coupling 0.002
energy spread 0.0013
bunch length 63 ps
off-set from stored beam orbit 10 mm
cf. booster synchrotron lattice: FODO. circumference: 400 m.
28-May-2008 Non-linear Beam Dynamics WS 13
Simulation Results• Decay rate of simulation is somewhat faster than that of
experiment.• Dependence of injection efficiency on ID gap is enough
described by simulation.
0.6
0.7
0.8
0.9
1
0 200 400 600 800 1000 1200
ID19
Inje
ctio
n E
ffic
ienc
y
Turn
12 mm13 mm14 mm15 mm16 mm18 mm20 mm
50 mm ~ 22 mm
0.6
0.7
0.8
0.9
1
0 500 1000 1500 2000
ID19
Inje
ctio
n E
ffic
ienc
y
Turn
12 mm
13 mm14 mm15 mm16 mm18 mm20 mm
50 mm ~ 22 mm
experiment simulation
28-May-2008 Non-linear Beam Dynamics WS 14
Lost Points of Injection Beam• Loss points detected by simulation.
50
100
150
0 500 1000 1500
ID19 gap = 50 mm (full open)ID19 gap = 12 mm (minimum)
Nu
mb
er o
f L
ost
Par
ticl
es
Path Length fron Injection Point [m]
0
Long straight sections
Long undulatorSeptum wall
(injection section)
ID 19 gap condition main loss points
minimum (12 mm) ends of undulator
maximum (50 mm)quadrupole magnets in matching section (highest vertical beta at upstream and down stream of long straight sections)
-10
0
10
20
30
40
50
60
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0 50 100 150
Bet
atro
n F
unc
tion
[m
]
Disp
ersion F
un
ction [m
]
Long Straight SectionNormalCG Cell
Path Length [m]
NormalCG Cell
xy
x
28-May-2008 Non-linear Beam Dynamics WS 15
Lost Particle Distribution in Initial Phase Space• Lost particle distribution in phase space of injection beam
detected by simulation.• Horizontal phase space: lost particles localize in large amplitude
side.• Vertical & longitudinal phase spaces: lost particles uniformly
distributed.
-0.015
-0.0075
0
0.0075
0.015
-0.2 -0.1 0 0.1 0.2
capturedlost
y' [
mra
d]
y (mm)
-0.005
-0.0025
0
0.0025
0.005
-80 -40 0 40 80
capturedlost
p /
ps (mm)
-0.6
-0.4
-0.2
0
0.2
0.4
-16 -14 -12 -10 -8 -6
capturedlost
x' [
mra
d]
x (mm)
28-May-2008 Non-linear Beam Dynamics WS 16
Beam Collimation in Transport Line• Beam collimator in horizontal direction was installed in transport
line from booster to storage ring to eliminate unnecessary beam tail.
= 0. 544mm = 1. 249mm
50
60
70
80
90
100
0 1 2 3 4 5 6
All ID Gap Full OpenAll ID Gap Full Close
Inje
ctio
n E
ffic
ien
cy [
%]
Collimator Gap (Half Width) []
booster
SR
28-May-2008 Non-linear Beam Dynamics WS 17
Influence of Chromaticity 1• Lowering the chromaticity improves injection efficiency.• In low chromaticity condition, ID gap dependence of the injection
efficiency is scarcely observed.
0.6
0.7
0.8
0.9
1
0 500 1000 1500 2000
ID19
Inje
ctio
n E
ffic
ienc
y
Turn
50 mm ~ 12 mm
0.6
0.7
0.8
0.9
1
0 500 1000 1500 2000
ID19
Inje
ctio
n E
ffic
ienc
y
Turn
12 mm
13 mm14 mm15 mm16 mm18 mm20 mm
50 mm ~ 22 mm
high chromaticity ( 8, 8 ) low chromaticity ( 2, 2 )
28-May-2008 Non-linear Beam Dynamics WS 18
Influence of Chromaticity 2
• Particle distribution in vertical direction– long undulator entrance.– after 500 revolutions.– without aperture limit.
10-1
100
101
102
103
104
105
-15 -10 -5 0 5 10 15
( x, y ) = ( 8, 8 )
( x, y ) = ( 2, 2 )
Nu
mb
er o
f P
arti
cles
y [mm]
0.6
0.7
0.8
0.9
1
0 200 400 600 800 1000 1200
( x, y ) = ( 8, 8 )
Inje
ctio
n E
ffic
ienc
y
Turn
12 mm13 mm14 mm15 mm16 mm18 mm20 mm
50 mm ~ 22 mm
ID19 gap
0.6
0.7
0.8
0.9
1
0 500 1000 1500 2000
( x, y ) = ( 2, 2)
Inje
ctio
n E
ffic
ienc
y
Turn
50 mm ~ 12 mmID19 gap
28-May-2008 Non-linear Beam Dynamics WS 19
Beta-Distortion Correction
• Beta-distortion was corrected by using 48 auxiliary qua
drupole magnet power supplies.
• Beta-distortion was measured by response matrix anal
ysis.
• Correction performance was checked by re-measurem
ent of beta-distortion after correction.
• It is observed beta-distortion correction improved inject
ion efficiency by about 15 %.
28-May-2008 Non-linear Beam Dynamics WS 20
Beta-Distortion Correction
before (rms distortion: 7.4%)
after (rms distortion: 1.9%)
0
10
20
30
40
0 100 200 300 400 500 600 700
x[m]
s [m]
0
10
20
30
40
0 100 200 300 400 500 600 700
x[m]
s [m]
* Half of the Ring is shown.
28-May-2008 Non-linear Beam Dynamics WS 21
Beta-Distortion Correction
before (rms distortion: 7.3%)
after (rms distortion: 1.5%)
0
20
40
60
0 100 200 300 400 500 600 700
y[m]
s [m]
0
20
40
60
0 100 200 300 400 500 600 700
y[m]
s [m]
28-May-2008 Non-linear Beam Dynamics WS 22
Influence of Beta-Distortion• Particle distribution in vertical direction
– beta-distortion correction ON/OFF.
– at long undulator entrance.
– without aperture limit.
0.4
0.6
0.8
1
0 200 400 600 800 1000 1200
with correction
Inje
ctio
n E
ffic
ienc
y
Turn
12 mm13 mm14 mm15 mm16 mm18 mm20 mm
50 mm ~ 22 mm
ID19 gap
0.4
0.6
0.8
1
0 500 1000 1500 2000
without correction
Inje
ctio
n E
ffic
ienc
y
Turn
12 mm13 mm14 mm15 mm16 mm18 mm20 mm
50 mm ~ 22 mmID19 gap
10-1
100
101
102
103
104
105
-20 -10 0 10 20
w/o correctionwith correction
Nu
mb
er o
f P
arti
cles
y [mm]
28-May-2008 Non-linear Beam Dynamics WS 23
Summary
• Injection efficiency at the SPring-8 storage ring was
investigated by experiments and simulations.
• Simulation well describes the experiments.
• Injection efficiency is mainly limited by vertical aperture.
• Following the implication by the simulation, we
improved the injection efficiency.– Injection beam collimator.
– Lowering chromaticity.
– Correction of beta-distortion.